The invention relates to a method for determining engine oil servicing dates for a motor vehicle engine as a function of recorded engine operating parameters.
A method is described in the Patent Specification DE 40 38 972 C1 for determining engine oil servicing dates for a motor vehicle engine as a function of recorded engine operating parameters, such as number of starts, crankshaft revolutions, driving and stationary periods, engine temperature, engine oil pressure, boost air pressure, oil consumption and fuel consumption, using an algorithm, which is not described in any more detail in the publication. The date is displayed by means, for example, of a series of light-emitting diodes or a digital display. In the method described in that publication, engine oil top-up processes are taken into account in the calculation of the servicing date by allowing the date to be delayed once by a defined period or a defined number of kilometers; it being possible to record the oil top-up amount quantitatively.
Methods for the automatic determination of engine oil quantity, such as are published in Offenlegungsschrift DE 44 29 234 A1 and German Patent Application No. 196 02 599.0, permit very reliable determination of the instantaneous engine oil quantity present even while the vehicle is in operation. By means, the oil consumption and the oil quantities added during oil changes or top-up procedures can be reliably recorded.
A method of the type mentioned at the beginning is described in Offenlegungsschrift EP 0 231 055 A2, in which the engine oil temperature is continuously recorded as the only operating parameter relevant to engine oil ageing and is used for evaluating the recorded engine revolutions, which procedure is carried out in this publication by means of a "penalty factor". Within a favourable engine oil temperature range, this penalty factor has the value of unity and, from there, it increases to larger values for both lower and higher engine oil temperatures. The result is that the actual total distance potential to the next recommended oil change is, at most, equally large and, generally speaking, is markedly less than the respective initially predetermined total distance potential.
The present invention is based, on the technical problem, of providing a method of the type mentioned at the beginning by means of which it is possible to determine, comparatively reliably, the date at which an engine oil servicing and therefore an engine oil change is desirable for a motor vehicle engine.
The present invention achieves this object by the provision of a method wherein one or more engine operating parameters relevant to engine oil ageing are continuously recorded by sensor means and associated evaluation factors are formed from them. The engine revolutions which have taken place are also recorded. In general, the concept of engine revolutions should be understood here to mean the revolutions of a crankshaft of the engine, which can for example be determined from the measured engine speed. The engine revolutions recorded are converted into a fictitious distance by evaluational association with the evaluation factors in accordance with a predeterminable association relationship. The remaining operating distance until a next engine oil servicing date is then calculated by subtracting this fictitious distance from a predeterminable total distance potential. It is found that this way of determining the engine oil servicing date by evaluating the revolutions of the motor vehicle engine as a function of the respective engine operating conditions presents a very reliable prediction of the appropriate engine oil usage time.
In the method according to the present invention special provision is made for the engine speed or the engine load to form a respective engine operating parameter relevant to engine oil ageing. It is found that a comparatively reliable estimate of the date for engine oil servicing or an engine oil change can be achieved by this means.
In another aspect of the inventive method, evaluation factors with respect to the engine oil temperature, the engine speed and the engine load and, as an option, the fuel consumption are determined on the basis of stored characteristic curves with which the engine revolutions are multiplied in order to obtain the fictitious distance. The evaluation factor characteristic curves can, for example, be determined on the basis of empirical values and/or the fundamental considerations familiar to the person skilled in the art with respect to the influences of the various engine operating parameters on the ageing of the engine oil.
According to another aspect of the invention, special provision is made for the total distance potential to be predetermined variably as a function of the oil quantity present directly after a previous oil change and/or of oil quantities added during oil top-up procedures. This makes it possible to take account of the fact that the total distance potential is, on the one hand, less for a smaller oil change quantity and, on the other hand, can be increased in the case of oil top-up processes as a function of their dates and the respective proportion of the freshly added oil quantity.
According to another aspect of the present invention, a calculation of a remaining operating period until a next engine oil servicing date takes place in addition to the remaining operating distance calculation, and independently of it, by subtraction of a determined fictitious oil use time from a specified initial operating period. The fictitious oil use time is then determined by associating the actual usage time since a previous oil change with a period evaluation factor which depends on the ratio of the fictitious distance determined to the distance actually travelled. By this means, flexible periodic servicing with respect to engine oil changes can be achieved depending on the driving style. This procedure also takes account of the fact that the engine oil ages to a certain extent when driving short distances, which makes engine oil changing desirable after a certain maximum use time at the latest, irrespective of the distance driven.